Non-Degenerate Two-Photon Absorption in ZnSe: Experiment and Theory

TL;DR

This study combines experimental measurements and theoretical modeling to analyze how non-degenerate two-photon absorption in ZnSe varies with frequency ratios and crystal orientations, revealing significant absorption enhancement.

Contribution

It provides the first comprehensive data set and theoretical analysis of non-degenerate two-photon absorption in ZnSe across different orientations and polarization states.

Findings

Absorption strength increases with non-degeneracy ratio.

Theoretical simulations match experimental data closely.

Orientation and polarization significantly affect absorption.

Abstract

We experimentally and theoretically investigate the non-degenerate two-photon absorption coefficient $\beta(\omega_1,\omega_2)$ in the prototypical semiconductor ZnSe. In particular, we provide a comprehensive data set on the dependence of $\beta(\omega_1,\omega_2)$ on the non-degeneracy parameter $\omega_1/\omega_2$ with the total frequency sum $\omega_1+\omega_2$ kept constant. We find a substantial increase of the two-photon absorption strength with increasing $\omega_1/\omega_2$. In addition, different crystallographic orientations and polarization configurations are investigated. The nonlinear optical response is analyzed theoretically by evaluating the multiband semiconductor Bloch equations including inter- and intraband excitations in the length gauge. The band structure and the matrix elements are taken an eight-band k.p model. The simulation results are in very good agreement with the experiment.